View Full Version : 308 AR - gas length question
About to start assembling a budget AR10 style rifle for a friend... first experience with this platform. I can't figure out the puzzle about how the gas length coordinates with the RE/buffer/spring. I've tried searches but haven't found the answer I'm looking for. Can you please help or post a link?
My friend wants a 20" barrel but collapsible stock. Can a 308 with rifle length gas reliably run using a carbine stock set-up?
I've seen bits about "Slash's" buffer with an AR15 RE (or something like that), but I chase them in cirlces and don't really find anything that ties together rifle gas with carbine stocks. Do I even need to worry about it?
I had hoped to buy a basic 308 carbine stock "kit" (from Armalite) but worried I'll run through several parts while experimenting until I finally get good function.
Primary purpose of the rifle is deer hunting. Seconds are recreational target shooting (600 yd or less) and cool factor. He's just always wanted one but doesn't really care about the details. He wants me to assemble it over time versus buying a complete rifle even though it'll cost more. I want to avoid using DPMS parts if I can help it.
The first thing you need to define is what you are going to build. Is it going to be an AR-10 based rifle or a 308 AR style rifle? You can't just mix and match all the parts of different manufacturers 308 AR rifles like you can with an AR-15.
The 20" AR-10 barrel will run with the AR-10 carbine buffer system. It uses a slightly longer receiver extension, AR-10 action spring (same for rifle and carbine) and a regular H3 buffer.
Gotcha, thanks Todd. I don't know the compatibilities between parts yet but at least found out that it matters... brand X won't work with brand Y, etc.
I wish I could with all Noveske but not in the cards on this one (I'll assemble my own later and will go down that route). This idea was more or less for an actual AR-10 based rifle... mostly a stock Armalite, just built pieces at a time. Thought I'd try out a Rainier Arms select barrel, free float with a JP Rifles handguard (have used on AR-15s and love them). LPK starting with basic Armalite and using their tactical 2-stage trigger, then helping my friend upgrade later when he'll have more appreciation (and coin). Armalite BCG.
He wants the basic collapsible stock for now but would like to change out to something "cooler" like an LMT SOPMOD he saw on one of my AR-15s. That's the other side of where I'm stuck... I think I read there's no issue in using a "regular" AR-15 stock on an AR-10 RE, but you won't be able to collapse it all the way. True? Sounds that way since it's slightly longer but must be the same diameter since you can use an H3 buffer.
OR, you can use an AR-15 RE, but then need a specially-weighted buffer (the one guys talk about from Slash or something), correct? And if so, which action spring do you use?
So no issues shooting rifle gas (Armalite pattern) on a carbine RE, then? I was worried about being undergassed...
caelumatra
09-08-11, 16:46
IMO its not worth the $100 for the slash buffer just so you can collapse the stock the whole way. With an ar10 collapsible RE you can't collapse the stock maybe...the last 1.5"
If you're shopping at rainier, get:
http://www.rainierarms.com/?page=shop/detail&product_id=1727
http://www.rainierarms.com/?page=shop/detail&product_id=1638
http://dsgarms.com/ProductInfo/ARMEC0120.aspx
That whole setup is less than the cost of the slash buffer. This is what I have in my MA Ten setup with a Noveske 18" and it shoots wonderfully
Add stock:
http://www.rainierarms.com/?page=shop/detail&product_id=1134
Slap this thing on it if you feel like
http://stores.homestead.com/Laruetactical/Detail.bok?no=501
Or just go with the SOPMOD since he likes yours
I think I read there's no issue in using a "regular" AR-15 stock on an AR-10 RE, but you won't be able to collapse it all the way. Correct
OR, you can use an AR-15 RE, but then need a specially-weighted buffer (the one guys talk about from Slash or something), correct? And if so, which action spring do you use? The spring is cut down. I'd say the AR-10 is enough bigger than an AR-15 that 3/4" of extra length collapsed stock shouldn't be an issue, if it is you should probably be looking at a 6.5 or 6.8 in the AR-15.
So no issues shooting rifle gas (Armalite pattern) on a carbine RE, then? I was worried about being undergassed... The AR-10 uses the same spring for rifle and carbine stocks, and the buffers are the same weight so it runs the same with rifle or carbine stock.
Thought I'd try out a Rainier Arms select barrel
Sorry to burst your bubble but if you aren't wanting to use DPMS parts you might want to rethink your barrel choice. The Rainier Select bbl is set up for DPMS gas length. I was also told these are for DPMS pattern bolts although the site doesn't specify. The Ultramatch bbls can be had for either DPMS or Armalite pattern, they have this option, Selects don't.
Select
http://www.rainierarms.com/?page=shop/detail&product_id=2692
Ultramatch
http://www.rainierarms.com/?page=shop/detail&product_id=2239
Sorry
You guys are awesome... thanks for the straight foward answers!
But sorry, here's another buffer/gas question... trying to make sure I understand so I don't have to ask again later:
So if AR-10 carbine and rifle buffers are the same weight and they use the same spring... and rifle-gas plays well with carbine buffer/receiver extension... and I assume that the length of spring travel or compression (or whatever you call it) is the same... then it means that the gas impulse has to be the same, right? So the gas port on each is sized to keep same impulse as the rifle with the other gas tube?
Which means the only reason for the different length buffers and REs is whether you go with traditional (A2) versus ninjafied (collapsible). Yes?
Sorry for the extreme nerd-out... I just don't feel good about dropping all the money without understanding what's happening on the inside.
Sorry to burst your bubble but if you aren't wanting to use DPMS parts you might want to rethink your barrel choice.
No worries... thanks for pointing it out. I hadn't looked back at the site for a week or two. I either forgot and meant the Ultramatch, or might have thought that DPMS pattern was compatible with Armalite uppers and BCGs. I guess that's a "no" then.
So to be clear, DPMS rifle gas does not equal "other" rifle gas?
I'll figure out a different barrel option if I have to... it's a deer rifle mostly, not a big deal.
Armalite Gas tube lengths for the AR10, if I'm not mistaken are slightly longer. DPMS uses AR15 length tubes.
Do not, DO NOT, use Bolts, BCGs and barrels interchangeably. Stick with one platform and go that route.
Do not, DO NOT, use Bolts, BCGs and barrels interchangeably. Stick with one platform and go that route.
Got it. Now just trying to figure out the compatibilities... so you said DPMS uses AR-15 length gas tubes, so all "DPMS pattern" barrels are out for me. My plan doesn't change much except that you helped me see I picked the wrong barrel.
Armalite upper
Armalite BCG
Need AR-10 barrel (Armalite... Rainier Ultramatch... Noveske?)
Thanks to you all I've got the stock/buffer/RE thing figured out. Will do AR-10 carbine style and not worry about losing the last notch or two on the collapse if my friend wants a fancy stock later.
turdbocharged
09-09-11, 06:34
Why not just build a lower and then purchase an upper to put on it?
Why not just build a lower and then purchase an upper to put on it?
I would but that's outside my friend's cash flow. He knows he's going to pay at least a few hundred $ more over the whole project but he wants/needs to spread it out over time. He might change his mind when I tell him how much a stripped barrel costs. If so, the only complete upper I know of that still fits the "budget build" category is Armalite. Others?
All signs point to a basic Armalite except that I'll assemble it myself. Maybe I should take his monthly "allowance", buy a stock rifle, and keep the $500 extra that it would have taken to build it, ha!
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